Research On Traitor Tracing Techniques

With the rapid development of digital technology and network technology, various forms of multimedia digital works(images, video, audio, etc.) have been distributed to subscribers in various types of networks, the copyright protection of which is becoming an urgent issue to be solved under the open application environment. In the broadcast encryption systems, such as pay-TV systems, on-line access to the database and CD distribution system, DS(Data Supplier) often face two representative threats: collusion key attacks and illegal replay attacks, the attackers in which are usually called traitors. Traitor tracing schemes are efficient methods for Data Suppliers to protect their copyrights against the above attacks and identify the traitors.Currently, the broadcast encryption is divided into the state broadcast encryption and stateless broadcast encryption. And stateless broadcast encryption with engineering application value can be divided into the symmetric key-based broadcast encryption and public key-based broadcast encryption. And the traitor tracing technology is mainly divided into the traitor tracing technology against collusion key attack and the traitor tracing technology against illegal rebroadcast attack. There are three kinds of traitor tracing schemes against collusion key attack, which are symmetrical traitor tracing schemes, asymmetrical traitor tracing schemes and threshold schemes; and there are two kinds of traitor tracing schemes against illegal rebroadcast attack, which are dynamic traitor tracing schemes and sequential traitor tracing schemes.In this dissertation, the traitor tracing technology for the broadcast encryption is systematically studied, and the main achievements of this dissertation are briefly listed as follows:1. Broadcast encryption technology is studied in detailed. How to minimize DS bandwidth requirements, the user key storage and the user key decoding complexity in the broadcast encryption scheme is a key issue. In this dissertation, a resilient broadcast encryption scheme based on secure frameproof codes is constructed, which is applicable for an especially broadcast encryption situation where the privilege user set has an upper bound. The scheme optimizes two parameters of the user key storage and the bandwidth requirements to finish the broadcast task even if DS transmits the encrypted message one time and the user stores only one key.2. Symmetrical traitor tracing technology against the collusion key attack is studied in detailed. The collusion key attack is a common attack mode in the broadcast encryption. In this dissertation, based on the broadcast encryption techniques and Hash function theory, a new three-level symmetrical scheme of traitor tracing is constructed which can combat with the collusion attack. Compared with the typical CFN schemes, the three-level scheme significantly optimizes the three main parameters, which are the user key storage, DS bandwidth requirements and the user key decoding complexity. The application-oriented broadcast encryption can be built using hash functions and specific sub-key value based on the three-level scheme.3. Asymmetrical traitor tracing technology against the collusion key attack is studied in detailed. The two problems of excessive user key storage and framing legal subscriber by DS in symmetrical schemes are considering. In this dissertation, an improved Asymmetrical traitor tracing scheme with automatic revoking is presented, in which the security scheme of session keys is constructed based on RSA and the security scheme of Enable Block(EB) is constructed based on discrete logarithm difficult and Oblivious Polynomial Evaluation protocol(OPE). The improved scheme possesses multi-service, anti-collusion, anti-framed and auto-revoking security features.4. Dynamic traitor tracing technology against the illegal replay attack is studied in detailed. The illegal replay attack is another common attack mode in the broadcast encryption. In this dissertation, a new dynamic traitor tracing scheme based on user set hierarchical structure is constructed, in which user IDs are marked by the watermarks and traitors are identified by the idea of layer by layer addressing. The new scheme can combat with the immediate rebroadcast attack efficiently and be applicable to the broadcast systems with different sizes of subscriber set by a balanced parameter, which has a certain theoretical value and copyright protection engineering value.